1. Field of the Invention
The present invention relates to communications. More particularly, the invention concerns a non-bandlimiting method and apparatus for sharing common antennas used to receive and transmit signals in a wireless communications network.
2. Description of the Background Art
A modern day communication network is required to support a variety of applications. One such communication network is a code division multiple access (CDMA) network that conforms to the xe2x80x9cTIA/EIA/IS-95 Mobile Station-Base Station Compatibility Standard for Dual-Mode Wideband Spread Spectrum Cellular System,xe2x80x9d hereinafter referred to as IS-95. The CDMA network allows for wireless voice and data communications between users. The use of CDMA techniques in a multiple access communication networks is disclosed in U.S. Pat. No. 4,901,307, entitled xe2x80x9cSPREAD SPECTRUM MULTIPLE ACCESS COMMUNICATION SYSTEM USING SATELLITE OR TERRESTRIAL REPEATERS,xe2x80x9d issued Feb. 13, 1990 and U.S. Pat. No. 5,103,459, entitled xe2x80x9cSYSTEM AND METHOD FOR GENERATING WAVEFORMS IN A CDMA CELLULAR TELEPHONE SYSTEM,xe2x80x9d issued Apr. 7, 1992, both of which are assigned to the assignee of the present invention and incorporated by reference herein.
In a CDMA network, a land-based data network can communicate with a subscriber station, typically a mobile cellular telephone, via one or more base stations. The base stations are communicatively coupled to the subscriber stations by a xe2x80x9cforward link.xe2x80x9d The subscriber station communicates with the land-based data network by transmitting data on a xe2x80x9creverse linkxe2x80x9d to a base station. A link is simply a communications connection used to transmit data from a source to a destination. The base station receives and routes received data, using a base station controller (BSC), to the land-based data network. For example, a subscriber station transmits a signal to the base station using an antenna and another antenna located at the base station receives the transmitted signal. This signal is processed and communicated further using the land-based data network. In a wireless network, a forward link and a reverse link may or, may not be allocated separate frequencies. Given the growing demand for wireless data applications, the need for very efficient wireless data communication networks have become increasingly significant.
To allow a network to handle more subscriber calls, the geographical area served by the communications network may be split up. These partitioned areas are called sectors or xe2x80x9ccells,xe2x80x9d and one or more base stations may be assigned to service the communications from subscriber stations located within any sector or sectors. Further, a signal received at an antenna may be routed to one or more base stations. As mentioned above, a base station (BTS) both receives and transmits communication signals. It is common for a BTS to have a single transmit signal and two receive signals, and to allow BTS transceiver subsystems from two different sectors to share an antenna.
To share antennas, a receive multi-coupler (RMC) 100 as shown in FIG. 1 is commonly used. Antenna 102 receives and transmits signals from the BTS to which the antenna 102 is connected. A surge protector 104 may be coupled to the antenna to prevent against unusual energy conditions, such as lighting striking the antenna. A duplexer 106 is coupled to the antenna 102 to facilitate the simultaneous transmission of signal 114 and the receipt of signals 116 and 118. Signal 114 is transmitted using antenna 102, and signals 116 and 118 are received using the antenna 102. A low noise amplifier (LNA) 108, a gain adjustment attenuator 110, and a power divider 112 are arranged to provide the signals 116 and 118. LNA 108 may also be connected to a fault detection unit 120. The design shown in FIG. 1 requires special filters, also referred to as duplexer 106, to split or combine signals using varying frequencies. Each of the signals 114, 116, and 118 are communicated to the base station using separate ports (not shown). FIG. 1 also shows a second arrangement within RMC 100 that works substantially as described above.
It is also common practice for a BTS to combine one transmit signal and one receive signal into one port rather than the multi-port configuration shown in FIG. 1. However, in this case, the RMC 100 as shown will not work. Another duplexer such as duplexer 106 would have to be added at the transmit/receive (TX/RX) inputs to separate a transmit signal from a received signal, and then use distinctly different and separate paths to route the signals. A path is a route between any two nodes, and may include more than one branch. This design separates the direction of the TX/RX signals, but does not consider the frequencies of the signals. Further, this modification to RMC 100 increases its cost and size, and reduces the performance of the unit.
What is needed is an invention that provides a method and apparatus that allows TX/RX signals to be processed using common hardware elements and substantially similar paths. The invention should allow a TX signal and a RX signal to be communicated to a base station using a common port, and provide for a received signal to be split and routed to a different base station using the same hardware.
The present invention is a method and apparatus that processes combined TX/RX signals using common hardware elements. The invention permits one port to commonly communicate a TX signal and a RX signal using a single port to a base station.
In one embodiment, the present invention comprises a non-band limiting method to share antennas where a signal to be transmitted is received at a first port. This first port is communicatively coupled to a base station. This xe2x80x9ctransmitxe2x80x9d signal travels from the first port through a plurality of direction units prior to being transmitted by an antenna. The direction units assure the transmit signal follows a desired path through the sub-network. Another signal is received at a second port communicatively coupled to an antenna. This xe2x80x9creceivedxe2x80x9d signal conceptually travels in a reverse direction to the transmit signal and through at least one of the direction units. The received signal shares a somewhat common path with the transmit signal, and is admitted to the base station at the same port that the transmit signal was received. The received signal is also split and received by a second base station.
In another embodiment, the invention may be implemented to provide an apparatus for sharing antennas that is non-band limiting. A transmit signal is received at a first port coupled to a base station. The transmit signal travels from the first port through a plurality of circulators prior to being transmitted by an antenna. A received signal is received at a second port communicatively coupled to the antenna. The received signal conceptually travels through the apparatus in a reverse direction to the transmit signal, through at least one of the circulator units, and is admitted to the transmitting base station using the same port from which the transmit signal originated. The received signal may also be split and received by a second base station.
The invention affords its users with a number of distinct advantages as found in its various embodiments. For example, one advantage is that the invention may be used in most wireless telecommunication networks where antenna sharing is desirable. Another advantage is that the direction, or path, of the transmit signal and the received signal are controlled, not the frequency of the signals. Still another advantage is that both the transmit signal and the received signal are processed using common hardware elements.